The primary objective of this research program is to study the role of I-region gene products of the mouse major histocompatibility complex in antigen presentation, specificity of cell interactions, and immune response regulation. This long-range objective will be accomplished in this project by the continued investigation of the relationship of Ia glycoproteins to Ir gene functions. Select groups of intra-I-region recombinant mice serve as models for the generation of Ir gene diversity. These recombinant strains are studied for altered Ir gene response patterns that would indicate an intragenic recombinant event, and such variants are characterized as to their specific "gain-loss" alterations by using monoclonal anti-Ia antibodies and biochemical analysis of immunoprecipitated Ia glycoprotein. The biochemical characterization of variant and parental Ia molecules is correlated with functional studies and Ia epitope mapping. During the past year, analysis of the immune responses of a panel of intra-I-region recombinant mouse strains to LDH-B and MOPC-173 demonstrated that B10.ASR7 and B10.BASR1 failed to mount T-cell proliferative responses to MOPC-173 and LDH-B, respectively. The parental strains that gave rise to the recombinants were high responders to both antigens. In addition to these studies, experiments investigating the Ir gene regulation of the type II antigen TNP-Ficoll demonstrated that the response is regulated by two loci, one in the I-A subregion and a second between S and D regions. A monoclonal antibody (48-21.7) was prepared that significantly blocked the response to TNP-Ficoll in the high responder b haplotype. This antibody immunoprecipitated a product of molecular weight = 40,000 that migrated slightly faster than a class 1 product recognized and precipitated by the anti-Db monoclonal anti-body B22/249. Sequential immunoprecipitation using these two monoclonal antibodies indicated that they precipitated distinct products. Such functional and structural analyses of intra-I-region recombinants are critical to our understanding of Ir gene function and the generation of Ir gene diversity, as well as the basis for T-cell recognition of class II glycoprotein complexes. (MB)